Hi there - I can recommend "The Bushman's Handcrafts" by R. M. Williams. Still in print. Your
local library may have a copy if the interest is fleeting . . . Tan barks from
native trees is covered, it recommends drying the bark, soaking in warm
water to see how dark the tannin is - aiming for a light tan; that depends on what you might use the skin for though
It deals with tanning, both veg and chrome then goes on to uses, including making a saddle, stranding and plaiting belts, "stringing" a bed frame with rawhide, it'll keep you out of mischief for ages.
Also you may care to research brain tanning - each animal is supposed to have sufficient grey matter to tan its hide.